PROJECT SUMMARY/ABSTRACT Over 50 million individuals suffer from arthritis in the US. Stem cell therapy can restore pain-free joints by regenerating rather than repairing cartilage defects. At the end of a successful cell transplant, cartilage defects should be replaced by hyaline cartilage that is indistinguishable from its native counterpart. Unfortunately, the transplanted cells often die in the hostile environment of an arthritic joint, which leads to formation of fibrocartilage and/or scars rather than hyaline cartilage. The inability to diagnose cell transplant failure in a timely manner represents a major barrier for the development of effective joint regeneration procedures. An imaging biomarker for stem cell engraftment or failure could improve our ability to identify the best-suited cell type and cell transplant procedure, and in turn could improve the success of novel cell therapies for arthritis treatment. Thus, our research project aims to develop an immediately clinically applicable imaging test to differentiate between viable and apoptotic matrix-associated stem cell transplants (MASI) in arthritic joints. To achieve this goal, we are utilizing clinically applicable iron oxide nanoparticles (ferumoxytol) for in vivo tracking of stem cells in arthritic joints. The first aim is to prove that ferumoxytol labeling provides critical information about engraftment or failure of MASI in an immune-competent large animal model. This supplement grant will enable inclusion of a black female scientist in our project. As an underrepresented minority in the STEM field (Science, technology, engineering and mathematics/medicine), participation of this minority researcher in our research studies will significantly enrich our team and the national scientific workforce. The proposed candidate will perform experiments under aim 1 with genetically engineered stem cells for targeted PET imaging. The candidate has extensive experience in genetic engineering and PET imaging of therapeutic cells, which will be highly beneficial for our project. The results can be immediately useful to track cell transplants in arthritic joints, understand the impact of iron labeling on stem cell engraftment outcomes, and predict the success of cell transplants in patients with MR imaging. Tracking MASI is important because it improves our understanding of the role of therapeutic cells in tissue regeneration processes. Results from this project will provide critical information about stem cell engraftment outcomes, accelerate the development of successful cell therapies for joint regeneration, and ultimately help alleviate long-term disabilities and related costs to our society.